Effective utilization of electric power has been called for against the recent trend of global warming. As one of means of effective utilization of electric power, secondary batteries for electric power energy storage have been expected, and from a viewpoint of air pollution prevention, it has been expected that large-size secondary batteries are put to early practical use as a power source for automobiles. Also, particularly with the proliferation and the performance improvement of electrical equipment, such as digital cameras and cellular phones, the demand of small-size secondary batteries as a power source for backup for computers and the like, or as a power source for small-size electrical household appliances is increasing steadily year by year.
As these secondary batteries, there is required a secondary battery having a performance corresponding to electrical equipment to be used, and, generally, lithium ion batteries are mainly used.
The lithium ion battery is configured such that a negative-electrode material in which a negative-electrode active substance, such as graphite, adheres to a negative-electrode substrate made of copper foil; a positive electrode material in which a positive-electrode active substance, such as lithium nickelate or lithium cobaltate, adheres to a positive-electrode substrate made of aluminum foil; a collector made of aluminum or copper; a separator made of a resin film, such as a polypropylene porous film; and an electrolytic solution, an electrolyte, and the like are enclosed inside an exterior can made of metal, such as aluminum or iron.
While the demand of lithium ion batteries is increasing, establishment of a countermeasure against environmental pollution due to used lithium ion batteries has been strongly desired, and collection of valuable metals and effective use thereof have been considered.
As a method for collecting valuable metals from a lithium ion battery having the above-mentioned structure, for example, dry treatment or incineration treatment, each being disclosed in PTL 1 and PTL 2, has been used. In this case, nickel, cobalt, and the like, valuable metals, are mostly reused for magnets, and the like.
However, dry treatment and incineration treatment have disadvantages that consumption of thermal energy is large and, moreover, lithium (Li) and aluminum (Al) can not be collected. There is also a problem with purity of collected metals, and accordingly the reuse of the collected metals for a lithium ion battery is difficult. Furthermore, there is another problem that, in the case where lithium hexafluorophosphate (LiPF6) is contained as an electrolyte, furnace materials are greatly consumed.
To solve these problems in dry treatment or incineration treatment, there has been proposed a method of collecting valuable metals by wet treatment, as disclosed in PTL 3 and PTL 4. A positive-electrode active substance is dissolved and refined by wet treatment, whereby the positive-electrode active substance can be recycled into Ni metal, Co metal, a metal compound, or a battery material. As this method by wet treatment, there has been proposed a total dissolution method such that all materials resulting from disassembling a lithium ion battery are dissolved by using an acidic solution or the like, and valuable metals are collected. However, in the case of this total dissolution method, a chemical agent is consumed for elements which excessively exist, such as aluminum, copper (Cu), iron (Fe), and the like, and therefore the method is not economical for effectively collecting valuable metals, such as nickel (Ni), cobalt (Co), lithium, and the like.
To solve this problem, there has been proposed a wet treatment using a selectively-peeling-off method, wherein a positive electrode material is selectively peeled off from a lithium ion battery, and valuable metals are efficiently collected from the positive electrode material. In the selectively-peeling-off method of a positive electrode material, generally, a first chemical treatment is such that a positive-electrode active substance containing valuable metals is peeled off from a positive-electrode substrate (positive-electrode foil) (made of Al, or the like). In the treatment of peeling off a positive-electrode substrate, an acidic or alkaline solution is used to peel off a positive-electrode active substance from a positive-electrode substrate. The peeled-off positive-electrode active substance contains trivalent Ni and trivalent Co. To leach Ni and Co, valuable metals, contained in the positive-electrode active substance, the positive-electrode active substance in solid form is made to change into that in liquid form, that is, in metal ion form, in an acidic solution, whereby valuable metals can be leached.
However, since trivalent valuable metals, such as nickel and cobalt, do not dissolve in an acid easily, the valuable metals cannot easily be made to be in metal ion form.
Thus, as a method of leaching out valuable metals, for example, as disclosed in PTL 5, there is a method wherein a reducing agent, such as a sulfite, is added to an acidic solution to make use of the reducing power of the reducing agent. This method enables a compound, such as LiCoO2, or LiNiO2, a positive-electrode active substance, to be decomposed into metal ions effectively and quickly, thereby leaching out valuable metals, such as nickel and cobalt, contained in the positive-electrode active substance.
In such valuable metal leaching method by wet treatment, before leaching out valuable metals, it is necessary to peel off a positive-electrode substrate made of aluminum or the like from a positive-electrode active substance, and this peeling-off causes dissolution of the positive-electrode substrate and accordingly requires a large amount of an alkaline solution. Also, in the leaching out of valuable metal, a reducing agent necessary for dissolution of a positive-electrode active substance requires an equimolar amount of electrons to Ni, Co, and the like, and therefore a more amount of the reducing agent needs to be added. Hence, in such valuable metal leaching method by wet treatment, a more amount of an alkali solution and a more amount of a reducing agent are used, and thereby the expense for leaching out valuable metals is increased accordingly, thus cost effectiveness is reduced.